1. Field of the Invention
The present invention relates to a structure, a method of manufacturing the structure, an imaging apparatus including the structure.
2. Description of the Related Art
Diffraction gratings having a periodic structure are used in various apparatuses as dispersive elements. In recent years, structures having a periodic structure made of a metal having high X-ray absorption are used in industrial applications such as nondestructive testing, medical applications such as roentgenography, and the like. Nondestructive testing and roentgenography exploit differences in X-ray absorption between elements contained in objects or living organisms or between differences in density therebetween to produce contrast images and are referred to as an X-ray absorption contrast method.
However, since light elements have extremely low X-ray absorption, it is difficult to image soft biological tissues or soft materials containing carbon, hydrogen, oxygen, and the like.
On the other hand, phase contrast methods using the phase difference between X-rays have been studied mainly in radiation facilities since the 1990s. Furthermore, phase imaging has been studied on a laboratory scale using X-ray tubes, thereby enabling a propagation method, a Talbot interference method, and the like in principle. In order to produce Talbot interference, a shield grating having a configuration in which X-ray permeable sections and X-ray shielding sections are periodically arranged is used. In the shield grating, the X-ray shielding sections include structures which are made of a metal, such as gold, having high X-ray absorption and which have a high aspect ratio (the aspect ratio is defined as the ratio (h/w) of the height or depth h to width w of each structure). A preferred method of manufacturing the shield grating is as follows: a mold is filled with a metal having high X-ray absorption by plating.
Japanese Patent Laid-Open No. 2010-185728 discloses a method in which a recessed section is formed in a silicon substrate by reactive ion etching and gold is precipitated in the recessed section by plating. In this method, a silicon oxide layer (electrically insulating layer) is formed over the bottom and wall of the recessed section by introducing an oxygen gas into an inductively coupled plasma treatment system and a portion of the silicon oxide layer that is located on the bottom is etched off, whereby a portion of the silicon substrate is exposed. The exposed portion is used as a seed layer during electroplating and gold is precipitated on the exposed portion.
However, a silicon oxide layer formed by introducing an oxygen gas into an inductively coupled plasma treatment system usually has a thickness of about 2 nm. Therefore, it is not necessarily easy for the silicon oxide layer, which serves as an insulating layer for electroplating, to keep sufficient insulation. In particular, in the case of forming a structure with a high aspect ratio, if a silicon oxide layer formed on a side wall thereof cannot keep sufficient insulation, voids (gaps) may possibly be formed because plating is precipitated on the side wall.